Synchronizing system



July 25, 1933.

c. E. HUFFMAN SYNCHRONIZING SYSTEM Filed Jan. 9, 1930 llllllillllllllll l-lllll I|||| Gun/n55 5 HVF'FMIHY Patented July 25, 1933 UNITED STATES PATENT OFFHCE CHARLES E. HUFFMAN, OF MONTG'LAIR, NEW JERSEY, ASSIGNOR TO JENKINS TELE- VISION CORPORATION, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF DELA- WARE SYN OI-IRONIZING SYSTEM Application filed January 9, 1930. Serial No. 419,497.

This invention relates to signalling methods and apparatus, and with particularity to method of synchronizing suitable for use in electro-optical transmission systems such as television, picture transmission, facsimile or the like.

The object of the invention is to provide a method of synchronizing receivers located at widely separated points with a central or transmitting set. It has been found that in such systems as television, picture transmission or the like, receiving sets may be synchronized with a transmitter by operating the driving motors of the receiving sets from the local commercial power supply mains. This is particularly true where the mains supply alternating currents. It is well known, however, that-in widely separated localities having alternating current supply 20 mains that the frequency of the supply-varies from time to time. For example in one 10- cality which may be designed to supply power current at 60 cycles per'second the central station generator may vary as much as one-tenth of one percent from the standard 60 cycles. This variation, of course, affects alike all the receivers that happen to be connected to these commercial supply mains. However, inf a diiferent locality where a diiferent central station is operated when it is attempted to operate receiving sets from the mains unless the central station generators in the separate localities hap-' pen to be operating precisely at the same frequency, it is obvious that only those receiving sets which are located in the same locality with the transmitter will synchronize therewith, it being understood of course that the transmitteritself is operated from the commercial supply mains. Accordingly it is a principal object of the present invention to provide amethodof synchronizing receiving sets with a transmitter Where the receiving sets are located in difi'erent sections supplied by different central power stations.

Another object of the inventionis to pro-,

vide a method of synchronizing wherein the speed of the transmitteris controlled by the commercial supply at difierent sections or localities.

Ateature of the invention'relates to the method of operating a central transmitter such as used in television, picture transmission, telegraphy and similar systems, wherein the motive power for the transmitter is arranged to be supplied alternately from a plurality of separate sections or localities.

Another feature of the invention relates to a system wherein a central transmitter such as a television transmitter or the like can serve a plurality of widely separated localities for the transmission of television or similar signals, without necessitating the transmission of special synchronizing signals from the central station, and without necessitating any complicated synchronizing apparatus by the individual receiving stations.

In achieving the above and other objects of the invention, the invention contemplates transmitting from the area in which the receiving apparatus is located, current having the desired frequency, and which is readily available from the commercial power network in that area, to the transmitter in order to synchronize said transmitter with the available frequency at the receiver.

Other features and advantages of the invention' not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims. 7

For the purpose of more clearly explaindrawing a schematic representation of 1 a central transmitting station and a plurality of receivers, certain of the receivers being located. in the same region as the transmitter and other receivers being located in a different region or in a region having a different commercial supply.

Referring to the drawing the numeral 1 represents a central transmitting station, and for the purpose of explanation it will be assumed that this station is a television transmitter in which case numeral 2 schematically represents any well known form of scanning apparatus having assoi ciated therewith the necessary driving motor, amplifier and radio apparatus. Inasmuch as this apparatus forms no feature of the present invention no further description thereof will be given. Suflice it to say that thetelevision analysis asis wellknown is dependentupon the speed of the driving motor which is adapted to be Connected to the commercial alternating current supply mains 3Pby me'ans'of conductors i and 5*and the switch apparatus- 6 when the latter is operated to the left. In the well known manner the image characteristics afterbeing analyzed are used to modulate a carrier wave by well known transmission methods, and these wavesta-re" impressed upon a transmitting antenna 7 to be picked up; at the different receiving localities. One

ofthese localities is represented by the dotted rectangle 8, and as shown in the drawing, this locality is supplied by the same commercial power mains- 3 as supply the central station 1-.- Threereceiving sets are indicated in the region 8, each set comprising,- well-known radio receiving apparatus, and any knownform of television repro- V ducing apparatus, each television set being provided with a driving motor (not shown) ceiving sets; in

in the well known" manner. In order that the television signals may be properly reproduced or indicated the driving motor must be run in perfect synchronisin with the driving motor at the central station It has been found that in localities employing alternating current that the television receiving: sets may beprovided with synchronous motors and that such synchronous motors will operate with sufficient accuracy to enablethe receiving sets to synchronize with the transmitter simply by connecting the synchronous motor at each receiving. set to the commercial sup a p y mains 3.- Numeral. 9 represents a different locality from 8, and having a central power statlon 10 separate from the power station 11 of the locality 8. It is natural, therefore, that since the power stations 10 andllare operated independently that the supply mains 12 in locality 9 may at various times be supplied with current of a diiferent freanency from that supplied to the mains onseduently if the motors forthereceiving sets of locality 9 are to be operated from the mains 12, it willbe clear that. the re this locality will not .be in synchronism with the transmitter '1.- I Inasmuch as one central station can serve a vast number of receiving sets located in widely separated localities, it has been proposed to eiiect synchronism at all the localities by transmitting from the central station a special set of synchronizing signals. It is obvious, however, that with such a system an enormous amount of power must be generated at the central station if the separated localities are to be supplied with the same amount of power necessary for synchronizing.

In accordance with the present invention, instead of attempting to synchronize the receivers with the transmitter, exactly the reverse is. in effect accomplished. For example, considering the locality 9 of the drawing and assuming that at any given instant the frequency of the supply from station 10 is 601 cycles and that the frequency of supply from station 11 is 59.9 cycles, it is obvious that if the switch 6 is operated to connect the transmitter motor to the mains 3 that the receiving sets in locality S will operate in synchronismwith the? transmitter, while the receiving sets in locality 9 will be out of synchronisnn However, if switch 6 is operated to connect the transmitting motor to the main L21, tl1enthe receiving, sets 1 in locality 9 will be in synchronism with the transmitter, V

In order that the central station 1 may serve both localities the invention contemplates driving thetransmitter meter at station 1 for a certain broadcasting. period during the day by connecting it to the mains 3-, and then for another broadcasting period connecting itto the, mains l2. 7 a

As a result of the foregoing arrangement thereceiving stationin the different localities may be provided with relatively simple and inexpensive motors; For example, if the mains 3 and 12 supply alternating current, then the television receiving. sets may :1

be driven synchronous motors which do not require any additional apparatus for maintaining them n step w1th the trans mitter.

While in the foregoing and in the drawing L the central station 1 isshown as connected to the mains 112: by physical wires,.it will be understoodthat this is merely illustrative and that any other manner of operating the central station equipment in accordance with the supply from mains 12 may be utilized, that is the central station transmitter motor maybe synchronized by means of a radio wave which bears modulations corresponding to the frequency of the current from the power station 10.

Various changes and modifications may be made in the system and apparatus disclosed without departing from the spirit and scope of the invention. the central station 1 is shown in the drawing as in the same zone as the locality 8, it will'be understood that said central station may be located in a region which is different from both thelocalities- 8 and the localities 9', inwhich case the central station transmitter will be alternately operated under control ofcurrents corresponding to; the commercial supply frequencies of the respective localities.

What is claimed is:

1. The method of synchronizing a central station message signal transmitter with a plurality of receivers situated in separate localities having difierent commercial supply mains which comprises alternately operating the receivers in one locality and the central station transmitter from the commercial supply mains of said locality, and then operating the receivers in the other locality and the central station transmitter from the commercial supply mains of said other locality.

2. The method of synchronizing a central station message signal transmitter with a plurality of receivers situated in separate localities having different commercial power networks which comprises alternately operating the central station'transmitter from the commercial supply networks of said localities.

3. The method of operating a central station message signal transmitter to serve a plurality of localities having different commercial supply networks which comprises operating the receiving sets in the same locality as the transmitter from the commercial supply mains therein and simultaneously with the operation of the transmitter, and then alternately operating the central station transmitter under control of the commercial supply network of another locality.

4. The method of operating a central station message signal transmitter to serve a plurality of localities having difl'erentcommercial supply networks which comprises operating the central station transmitter for one period under control of the commercial supply network of its locality and then alternately operating the central station transmitter for another period under control of the commercial supply network of another locality.

5. The method of operating a central station television transmitter to serve a plurality of separate localities having different commercial supply frequencies which comprises alternately operating the central station apparatus under controlof the commercial supply frequencies of diiferent localities.

6. The method of operating a television transmitter to serve a distant locality having a different commercial supply frequency from that of the locality wherein the transmitter is located which comprises controlling the speed of the transmitting apparatus in accordance with the frequency of the supply in said distant locality.

7. The method of operating a television transmitter to serve a distant locality having a different commercial supply frequency from that of the locality wherein the transmitter is located, which comprises transmitting from the commercial supply in the distant locality to the television transmitter synchronizing currents having a frequency determined by the supply frequency of said distant locality.

8. The method according to claim 7 in which the synchronizing currents are transmitted by radio.

9. In a television system the method of synchronizing which comprises operating a central message transmitter under control of a current commercial supply common to a plurality of receiving sets at a distant locality, which supply is of a different frequency from that in the locality of the transmitter. 1

' 10. In a television system the combination of a central station transmitter, a television receiver situated in a locality having a different commercial supply frequency from that of the transmitter, and means for operating the transmitter under control of the supply frequency in the locality of the recelver;

' CHARLES E. HUFFMAN. 

